This invention relates to an induction system for an internal combustion engine and more particularly to an improved cylinder head and induction passage arrangement for a multiple valve internal combustion engine.
It has been recognized that the performance of engines can be improved by increasing the number of valves serving each cylinder of the engine. Four valve per cylinder engines employing two intake valves per cylinder are now common practice, particularly in the automotive industry. However, it is also acknowledged that greater performance can be obtained through the use of three intake valves per cylinder. However, the use of three intake valves per cylinder does give rise to certain problems in that the flow through the three intake valves can cause interfering relationship within the cylinder under some conditions and can adversely affect performance.
For example, in a normal three input valve engine there are provided a pair of side intake valves that are disposed on opposite sides of a first plane that lies on the cylinder bore axis and which are intersected or lie close to a second plane perpendicular to the first plane and also passing through the cylinder bore axis. A third or center intake valve is disposed on the first plane and is spaced further from the second plane than the pair of side intake valves.
With this type of valve placement, the side intake valves can be disposed so as to generate a tumble action within the cylinder which has been found to promote performance, particularly under low and mid-range performance. This tumble action directs the charge into the cylinder in such a way as to cause a swirl about an axis that extends transversely to the cylinder bore axis and is thus distinguished from more conventional, axial swirl which occurs around the cylinder bore axis.
It has been found, however, that the positioning of the center intake valve creates a reverse tumble action which obscures or reduces the tumble action which is generated by the side intake valves and can under some running conditions deteriorate engine performance.
It is, therefore, a principal object of this invention to provide an improved induction system arrangement for an engine employing three intake valves per cylinder.
It is a further object of this invention to provide a cylinder head and intake passage arrangement for a three intake valve per cylinder engine wherein the effects of tumble in low and mid-ranges can be maintained.
In addition to the desirability of maintaining a tumble action in the cylinder under some running conditions, it is also desirable to employ a control valve for controlling the flow through the various intake valves. By doing this, it is possible to tune some of the intake passages to suit running conditions substantially different than those of the remaining valves. However, in order to do this, it is necessary to provide intake passages of different lengths and with previously proposed multi-valve constructions, this has not been easy to accomplish.
It is, therefore, a still further object of this invention to provide a cylinder head and induction passage arrangement for a multi-valve engine wherein the passages can be configured so as to have substantially different lengths without interfering with each other and while still maintaining a compact construction.
With the use of multi-valves and multiple intake passages to achieve the aforenoted result, it is the practice to provide at least one intake passage that is separate from the remaining intake passages that serve the cylinder. However, total isolation between the intake passages, particularly where one of them is throttled, can give rise to some performance defects in mid-range conditions where at the transition between the flow between only certain of the intake passages and flow between all of the intake passages.
It is, therefore, a still further object of this invention to provide an improved cylinder head and intake passage arrangement for a multiple valve engine that will provide good performance throughout the entire engine speed in low ranges.